1. Field of the Invention
The invention relates to an apparatus and a method for manufacturing an electricity storage material.
2. Description of Related Art
In recent years, lithium ion secondary batteries have been used for hybrid vehicles, electric vehicles, etc. Electrodes of the lithium ion secondary batteries are manufactured by first kneading powder of an active material etc. and a solution of a thickener to produce slurry of an active material (electricity storage material), and then applying the slurry to a base material such as aluminum foil and drying the slurry. Japanese Patent Application Publication No. 2011-113821 (JP 2011-113821 A) describes a method for predicting battery performance by measuring a change in impedance of slurry of an active material with time in the step of drying the slurry, and analyzing an aggregation process of particles dispersed in the slurry. Satisfactory battery performance is obtained in the case where the impedance of the slurry decreases monotonically.
How much a powder thickener has been dissolved in a liquid solvent is important to the battery performance. The rate of the mass of solute dissolved in a certain amount of solvent to solubility (the maximum mass of solute that can be dissolved in the solvent) is herein referred to as the “dissolution rate to solubility.” In order to obtain satisfactory battery performance, it is necessary to use a solution of a powder thickener dissolved in a liquid solvent at a dissolution rate to solubility of, e.g., 80% or more. A conventional kneading step requires time and effort as a kneading device is stopped during kneading to take out the solution, and viscosity of the solution is measured to determine the dissolution rate to solubility.